1. Field of the Invention
This invention relates to heat developable photographic materials and processes for providing a dye enhanced silver image. In one of its aspects it relates to a heat developable photographic element for providing such a dye enhanced silver image comprising a support having thereon in reactive association certain layers for producing the described dye enhanced image. In another of its aspects it relates to a process for providing such a dye enhanced silver image by merely heating the described heat developable material.
2. Description of the State of the Art
It is well known to provide a silver image in a heat developable material, also known as a photothermographic material, using processing with heat. After imagewise exposure, the resulting latent image in the heat developable material is developed and, in some cases, stabilized, merely by uniformly heating the heat developable material. This heat development can provide a silver image. Such heat developable materials and processes are described, for example, in U.S. Pat. No. 3,301,678 of Humphlett et al, issued Jan. 31, 1967; U.S. Pat. No. 3,152,904 of Sorenson et al, issued Oct. 13, 1964; U.S. Pat. No. 3,392,020 of Yutzy et al, issued July 9, 1968; and British Pat. No. 1,161,777 published Aug. 20, 1969.
Certain photothermographic materials are also known for producing a developed image in color as described, for example, in U.S. Pat. No. 3,531,286 of Renfrew, issued Sept. 29, 1970 and U.S. Pat. No. 3,761,270 of deMauriac and Landholm, issued Sept. 25, 1973. In these color-forming materials, a color-forming coupler is required to provide the color image.
Thermographic materials are also known for providing an image in color. The image is provided by imagewise heating such materials. Such thermographic materials are described, for example, in U.S. Pat. No. 3,094,417 of Workman, issued June 18, 1963 and U.S. Pat. No. 3,592,650 of DeSelms, issued July 13, 1971. These are not useful for photographic processes requiring the photographic speed of photosensitive silver halide in which a latent image is provided by imagewise exposure to light. In addition, colored film materials are known which can be made clear or colorless in image areas when heated thermographically. These can comprise, for example, a mild reducing agent in combination with an amine compound. These thermographic materials are described, for example, in U.S. Pat. No. 3,852,093 of O'Leary, issued Dec. 3, 1974. These thermographic materials also lack the desired photosensitivity of heat developable photographic materials. Use of heat to change an antihalation layer to colorless is described in, for example, U.S. Pat. No. 3,769,019 of Weise and VanDyke Tiers issued Oct. 30, 1973. This described heat bleaching is not employed to provide enhancement of a silver image, but rather is employed for antihalation purposes.
It has been proposed in certain photographic materials to use the oxidized form of certain compounds to react with other components of the material to change the color of the resulting image. For example, in a diffusion transfer photographic material, oxidized developer can be diffused to a contiguous layer. This is described, for example, in U.S. Pat. No. 3,185,567 of Rogers, issued May 25, 1965. This, however, does not relate to heat developable photographic materials.
In a heat developable photographic material it is also known to incorporate a 3-pyrazolidone compound in the material with a silver halide photosensitive emulsion. This compound can be used in a process carried out by contacting a negative layer containing the developing agent before heat development with a positive layer containing a colorless triazolium compound. This is described, for example, in U.S. Pat. No. 3,257,205 of Cassiers et al, issued June 21, 1966. In this process the unreacted developer is used to reduce the colorless material such as a silver salt or a tetrazolium salt to silver metal and dye respectively. This results in the case of the silver salt in a negative scale in silver in the emulsion layer and a positive scale in silver in a receiving layer provided. In the case of the tetrazolium salt, a negative image in silver in the emulsion layer and a positive dye image in the receiver can be obtained. If these layers remain together, they are not useful and must be separated to give both negative and positive images. In this sense, it is not possible to provide for dye enhancement of the silver image in the emulsion layer as described in this patent.
In photographic materials processed in processing solutions or baths, it has been known to provide a dye image which reinforces a silver image formed upon development. This is described, for example, in British Specification No. 1,096,049 published Dec. 20, 1967. This concept, however, has not been used in heat developable photographic materials.
It is known in photographic materials as described, for instance, in U.S. Pat. No. 2,071,688 of Gaspar, issued Feb. 23, 1937 to form a dye over the entire extent of the layer in which it is formed by a reaction wholly independent of the silver image and then to destroy the resulting dye at the points of the silver deposit or at points which are free of the silver deposit. This concept is also described in U.S. Pat. No. 2,041,827 of Gaspar, issued May 26, 1936. It is indicated that a photographic layer containing a silver image can be impregnated with a hydra azo substance and then this hydra azo substance can subsequently be converted into an azo compound. At the point at which the dye is to remain invisible, the azo dye produced can be destroyed locally and this can take place at the points of the silver or the points free of silver in the layer. In each case, however, the image is formed with processing solutions or baths. Also, any dye destruction in the photographic material is by the silver image and not by the unused developer that may be employed.
It is also known to incorporate stabilizer precursors in heat developable photographic materials for processing with heat. Certain sulfur-containing compounds may be heat activated to stabilize an image in a photographic element as described, for example, in U.S. Pat. No. 3,301,678 of Humphlett et al, issued Jan. 31, 1967. The sulfur-containing compound, it is believed, breaks down or "cleaves" at elevated temperatures to form a compound that combines with the silver halide in the unexposed and undeveloped areas of the emulsion. The resulting silver mercaptide is more stable than silver halide to light, atmospheric and ambient conditions. However, no indication is given that such stabilizer precursors can be useful in a material which provides for image enhancement with dye.
In U.S. Pat. No. 4,012,260 of D. G. Dickerson and P. B. Merkel and in Research Disclosure, Volume 140, December 1975, Item 14049, published by Industrial Opportunities Ltd., Homewell, Havant, Hampshire, P09 1EF, UK, certain carboxylate compounds are described as activator-stabilizer precursors in heat developable photographic materials. Upon heating, such compounds release an agent that is capable of activating a developer and also release a moiety capable of stabilizing a silver halide image. U.S. Pat. No. 4,060,420 of Merkel and Ling also describes certain activator-stabilizer precursor compounds which are useful in a photographic material which is responsive to heat for processing. The activator-stabilizer precursors are characterized by the fact that they are acid byproducts having reduced toxicity and volatility and other advantages. The described activator-stabilizer precursors have a base portion and an acid portion wherein the acid portion is an .alpha.-sulfonylacetate. Especially useful .alpha.-sulfonylacetate compounds include bis(2-amino-2-thiazoline)methylene(sulfonylacetate), N-(2-thiazolino)-N'-(imidazolino)ethylenediamine ethylenebis(sulfonylacetate) and 1,3-bis[2S-(N,N'-ethyleneisothiourea)ethyl]urea ethylenebis(sulfonylacetate). These activator-stabilizer precursors, however, do not provide an answer to the problem of providing enhanced images by other than formation of further developed silver.
There has been a continuing need to provide improved efficiencies in image formation and use of development products in heat developable photographic materials. There has also been a need to provide improvements in reduction of the concentration of silver needed to provide a desired image in such heat developable materials. Further, there has been a need to provide increased efficiency to enable further use of larger grain silver halide materials to reduce the amount of exposure required to provide a desired image in heat developable photographic materials.